1. Field of the Invention
The subject invention relates to the recording of electric signals and, more specifically, to methods and apparatus for recording electric signals on a light sensitive recording medium with the aid of electrically switchable light gates.
2. Disclosure Statement
This disclosure statement is made pursuant to the duty of disclosure imposed by law and formulated in 37 CFR 1.56(a). No representation is hereby made that information thus disclosed in fact constitutes prior-art inasmuch as 37 CFR 1.56(a) relies on a materiality concept which depends on uncertain and inevitably subjective elements of substantial likelihood and reasonableness, and inasmuch as a growing attitude appears to require citation of material which might lead to a discovery of pertinent material.
The photosensitive component, such as the silver halide system, used in photosensitive oscillograph papers or other photographic materials, has its highest sensitivity in the far blue and ultraviolet range; that is, at wavelengths below 475 nm (nanometers). Of course, photographic materials are frequently sensitized by dyes or otherwise rendered panchromatic to have a light sensitivity above the basic sensitivity of the photosensitive component. However, especially in the case of photosensitive oscillograph papers or other photographic recording media, the far blue and ultraviolet region is frequently relied on for high-sensitivity response.
In practice, such preference as to the recording medium is paired with a growing choice of the mercury arc lamp as light source for oscillograph apparatus and other light recording equipment. In fact, the mercury arc lamp which strongly radiates in the blue and ultraviolet region and photosensitive paper having a basic sensitivity in the same region, form a team in practice in a large number of oscillograph and other light recording apparatus.
In the context of oscillograph and other light recording apparatus, use has recently been made of electrooptically active solid-state materials for selectively gating light to the recording medium.
In this respect, various electrooptical light gate systems have been proposed for diverse fields of utility. For instance, an article by J. Thomas Cutchen et al, entitled Electrooptic Devices Utilizing Quadratic PLZT Ceramic Elements, published in 1973 Wescon Technical Papers, Vol. 17, part 30, pp. 30/2 et seq., and an article by the same authors entitled PLZT Electrooptic Shutters: Applications, APPLIED OPTICS, Vol. 14, No. 8 (August 1975), pp. 1866 et seq., describe electrooptic ceramics and devices employing transparent lanthanum-modified lead zirconate titanate (PLZT), and applications thereof, including page composers, display devices, eye protection devices, industrial welding protection, large aperture photographic shutters and variable density filters. Reference is also made to the extensive bibliography of these two articles, hereby incorporated by reference herein.
Facsimile apparatus for writing and reading mechanically moving documents with an electronically controllable switching mask plate, disposed between polarization filters and consisting of a material containing mixed crystals of lead zirconate and lead titanate, and doped with lanthanum, and provided with aligned electrodes, was proposed in U.S. Pat. No. 3,930,119, by Rolf Schmidt et al, issued Dec. 30, 1975.
A further proposal is apparent from British Patent Specification No. 1,534,027, by Battelle Memorial Institute, published Nov. 29, 1978. That proposal employs electrooptical light modulating devices preferably made of a PLZT ceramic material.
Improved light gate utilization methods and apparatus, with special optical systems, were disclosed in German Patent Publication No. 28 09 997, filed by the subject assignee, published Sept. 21, 1978, and herewith incorporated by reference herein.
Radically different from these proposals to employ PLZT and similar electrooptically active solidstate materials for light gating purposes are proposals to employ such materials for optical information storage or recording, with the particular material constituting the storage or information recording medium itself.
Reference may in this respect be had to an article by F. Micheron et al, entitled Holographic Storage in Quadratic PLZT Ceramics, Journal of the American Ceramic Society, Vol. 57, No. 7, pp. 306-08, an article by F. Micheron et al, entitled Optical Recording of Digital Data in PLZT Ceramics, Applied Physics Letters, Vol. 24, No. 12 (June 1974), pp. 605-07, an article by J. M. Rouchon et al, entitled Photoinduced Changes of Refractive Index in PLZT Ceramics, Ferroelectrics, Vol. 11 (1976), pp. 389-92, an article by A. E. Krumins et al, entitled Optically Induced Birefringence Change in La-Doped Lead Zirconate-Titanate Ferroelectric Ceramics, Ferroelectrics, Vol. 18 (1978), pp. 21-26, an article by L. S. Kamzina et al, entitled Photoinduced Phenomena in Lead Magnesium Niobate Crystal at the Diffuse Phase Transition, Ferroelectrics, Vol. 18 (1978), pp. 113-16, and an article by A. P. Levanyuk et al, entitled Theory of Photoinduced Changes in Refractive Index and Spontaneous Polarization, Ferroelectrics, Vol. 18 (1978), pp. 147-51.
In their above mentioned articles, Micheron et al and Rouchon et al report on techniques for holographic storage and optical recording in PLZT ceramics through photoinduced birefringence, and for an erasure of such recordings or of the photoinduced berefringence through illumination of the PLZT sample in the absence of an applied electric field. In particular, Micheron et al have pointed out that optical erasure with no external filed applied may be considered as a second recording. Krumins, Kamzina, Levanyuk et al report on similar experiments and supply theoretical explanations.
In the manufacture of PLZT electroded wafers, a suspension of light gating properties was observed when the wafers were subjected to ultraviolet exposure for cleaning purposes. This so-called "temporary UV blindness" disappeared upon annealing at 100.degree. C. for one hour.
Prior to the subject invention, no connection was apparent between the above mentioned observations and theories on the one hand and a reduction of the light transmission of electrooptical solid-state light gates, particularly of the PLZT or ferroceramic type, upon prolonged operation, on the other hand.
Rather, the rule of thumb developed that the interelectrode spacing, that is, the spacing between immediately adjacent electrodes, should not be smaller than the thickness of the layer of electrooptically active material. It now appears in retrospect that the latter relationship provided a favorable distribution of the applied electric fields throughout the thickness of the electrooptically active material, thereby reducing what has now been recognized as photoinduced birefringence. However, the latter rule of thumb has continued to place severe restrictions on a reduction of interelectrode spacing for a given thickness of the electrooptically active substrate or layer, impeding attainment of desirable properties, such as high resolution.